1. Field of the Invention
The present invention relates to an image forming apparatus and, more particularly, to cleaners of a transferring device to transfer a toner image formed on a photosensitive drum onto a sheet of paper conveyed by adsorbing it to a transferring belt which also functions as a conveying means.
2. Description of the Related Art
In recent years, remarkable progress is observed in the digitization of electro-photographic apparatus and digital data used copiers using digital data comprising images have been widely used. So-called reversal developing system is mainly used for digital copiers and in the transferring process, polarity of a photosensitive drum and that of a transferring member such as a transferring corona are set so that they become different each other.
Accordingly, polarity of a sheet of paper as an image receiving medium and that of a photosensitive drum are reversed and attracted to each other and a paper is adsorbed to the photosensitive drum. So, it becomes necessary to devise a means to separate a sheet of paper from the photosensitive drum.
In conventional laser printers so far available, the process speed of many of them is slow and a small diameter is sufficient for a photosensitive drum and a paper can be separated by its stiffness and further, if necessary, a separation charger is provided as an auxiliary means at the downstream side of a transfer corona, and a paper is discharged to a degree not to disturb a toner image transferred on a sheet of paper.
However, digital copiers have fast process speed and it is required to make the diameter of photosensitive drums large. Therefore, separation of paper by its stiffness becomes difficult.
So, a system has been proposed to transfer a toner image on a photosensitive drum onto a sheet of paper using a transferring belt as a transferring member while conveying the paper by adsorbing it to the transferring belt.
However, when the transferring belt is used as a transferring member, a non-image area of a photosensitive drum contacts directly the transferring belt and after generating a so-called jam, the photosensitive drum having a toner image may contact directly the transferring belt. Because of this, it is indispensable to install a belt cleaner to clean the transferring belt.
As a belt cleaner, a blade cleaner using a blade formed with a rubber elastic body is used in many cases from cost and easiness of construction. As a demerit of a blade cleaner, it can be pointed out that the coating layer of the surface of the transferring belt may be injured as stress applied to the transferring belt is relatively large.
When the coating layer of the transferring belt is injured, the blade edge is damaged and the defecting cleaning is generated. Because of this, it is necessary to mount a lubricant applying mechanism separately to obtain a stabilized cleaning performance in the use for a long period.
From such a problem, many brush cleaners using a conductive brush are proposed as a cleaning member. However, for instance, for removing a large amount of toner after generating jam, a relatively long warm-up time is needed and in addition, there will be generated a problem that it becomes very difficult to remove toner entered into a conductive brush. Therefore, in the use for a long period, there is generated a problem that the back side of a paper is stained by a toner discharged from a conductive brush.